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<div class='page-title'>Javadoc all exceptions</div>

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<br>All exceptions thrown by a method can be documented with the <tt>@throws</tt>
javadoc comment (same as <tt>@exception</tt>). Some argue that an&nbsp;<tt>@throws</tt>
should be included for every thrown exception, since it is the only way
to clearly state all requirements made upon the caller (the pre-conditions).
However, <a href="TopicActioncd9b-2.html">others disagree</a>.
<p>If all <tt>null</tt> object parameters passed to class methods cause
a <tt>NullPointerException</tt>, then it is acceptable to state this once
in the class javadoc comment, instead of repeating it for every method.
Another alternative is to state in <tt>overview.html</tt> (javadoc's summary
description of an application) that all parameters are to be considered
as non-null unless explicitly stated otherwise.

<p><b>Example</b>
<p>This example has an unusually large number of pre-conditions. Remarks
regarding <tt>NullPointerException</tt> are placed in the class level javadoc
comment.
<p>Note that the unchecked <tt>SecurityException</tt> is thrown indirectly,
through the calls to the methods of the <tt>File</tt> class.
<br>
<PRE>

<span class='keyword'>import</span> java.io.*;

<span class='comment'>/**
* If a null object parameter is passed to any method, then a
* &lt;code&gt;NullPointerException&lt;/code&gt; will be thrown.
*/</span>
<span class='keyword'>public</span> <span class='keyword'>class</span> WriteTextFile {

  <span class='comment'>//..other methods elided
</span>
  <span class='comment'>/**
  * Change the contents of a text file in its entirety, overwriting any
  * existing text.
  *
  * @param aFile is an existing file (not a directory) which can be written.
  * @param aContents is the text to be placed into aFile.
  *
  * @exception FileNotFoundException if aFile does not exist.
  * @exception IOException if stream to aFile cannot be written to or closed.
  *
  * @exception IllegalArgumentException if aFile is a directory.
  * @exception IllegalArgumentException if aFile cannot be written.
  * @exception SecurityException if a SecurityManager exists and
  * disallows read or write access to aFile.
  */</span>
  <span class='keyword'>static</span> <span class='keyword'>public</span> <span class='keyword'>void</span> setContents(File aFile, String aContents)
                                 <span class='keyword'>throws</span> FileNotFoundException, IOException {
    <span class='keyword'>if</span> (aFile == <span class='keyword'>null</span>) {
      <span class='keyword'>throw</span> <span class='keyword'>new</span> NullPointerException(<span class='literal'>"File must not be null."</span>);
    }
    <span class='keyword'>if</span> (aContents == <span class='keyword'>null</span>) {
      <span class='keyword'>throw</span> <span class='keyword'>new</span> NullPointerException(<span class='literal'>"Contents must not be null."</span>);
    }
    <span class='keyword'>if</span> (!aFile.exists()) {
      <span class='keyword'>throw</span> <span class='keyword'>new</span> FileNotFoundException (<span class='literal'>"File does not exist: "</span> + aFile);
    }
    <span class='keyword'>if</span> (!aFile.isFile()) {
      <span class='keyword'>throw</span> <span class='keyword'>new</span> IllegalArgumentException(<span class='literal'>"Must not be a directory: "</span> + aFile);
    }
    <span class='keyword'>if</span> (!aFile.canWrite()) {
      <span class='keyword'>throw</span> <span class='keyword'>new</span> IllegalArgumentException(<span class='literal'>"File cannot be written: "</span> + aFile);
    }

    Writer output =  <span class='keyword'>new</span> BufferedWriter( <span class='keyword'>new</span> FileWriter(aFile) );
    <span class='keyword'>try</span> {
      output.write( aContents );
    }
    <span class='keyword'>finally</span> {
      <span class='comment'>//flush and close both "output" and its underlying FileWriter
</span>      output.close();
    }
  }

  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>void</span> main (String... aArguments) <span class='keyword'>throws</span> IOException {
    File testFile = <span class='keyword'>new</span> File(<span class='literal'>"C:&#092;&#092;Temp&#092;&#092;blah.txt"</span>);
    setContents(testFile, <span class='literal'>"blah blah blah"</span>);
  }
} 
</PRE>
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<div class='topic-section'>See Also :</div>
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  <a href='TopicAction5d11-2.html?Id=5'>Validate method arguments</a> <br>
 
  
  <a href='TopicActioncd9b-2.html?Id=171'>Avoid @throws in javadoc</a> <br>
 
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